You see, happiness ain’t a thing in itself — it’s only a contrast with something that ain’t pleasant. That’s all it is. There ain’t a thing you can mention that is happiness in its own self — it’s only so by contrast with the other thing. And so, as soon as the novelty is over and the force of the contrast dulled, it ain’t happiness any longer, and you have to get something fresh.

Mark Twain (1835-1910) American writer [pseud. of Samuel Clemens]

Story (1868?), “Extract from Captain Stormfield’s Visit to Heaven,” Part 1, Harper’s Monthly Magazine, Vol. 116, No. 691 (1907-12)
    (Source)

Sam Bartlett to the narrator about why there is pain and suffering in Heaven (so that there can be happiness as a contrast).

First published in book form in 1909. More about the writing and publishing history here.